Enhanced reconditioning equalizer filter chain for multi-carrier signals

ABSTRACT

A technique for enhanced reconditioning equalizer filter chain for multi-carrier signals is described. The input to a transmitter chain is modified by an enhanced reconditioning equalizer filter chain, prior to being applied to the transmitter. The enhanced reconditioning equalizer filter chain modifies and smoothen the amplitude of the signal. The modified and smoothen signal has its picks reduced which results to lower Crest Factor. The input to the enhanced reconditioning equalizer filter chain could be a baseband, an intermediate frequency (IF) or radio frequency (RF) signal. When the signal is an IF or RF signal it needs to be down converted to baseband before applied to enhanced reconditioning equalizer filter chain. The enhanced reconditioning equalizer filter chain could be implemented in digital or analog domain.

This application is a continuation-in-part of U.S. patent applicationSer. No. 10/782,158 filed Feb. 20, 2004 now U.S. Pat. No. 7,305,041.

BACKGROUND OF INVENTION

The present invention relates to an enhanced reconditioning equalizerfilter chain to boost the performance of any multi-carrier communicationtransmitter. The enhanced reconditioning equalizer filter chain inputcould be baseband, intermediate frequency (IF), or RF signal, and itsoutput is the peak reduced and smoothen baseband signal that can be upconverted to IF or RF. In any wireless communication system one of thecritical sub-systems is the transmitter. This sub-system has a majorcontribution in cost, power consumption, and size of the system. Themain reason is the requirement of multi-carrier communicationtransmitter sub-system for linear components. The higher the linearity,the higher the power consumption, cost and size. In order to minimizethe cost, size and power consumption there is a need for techniques thatovercome this problem. This invention conquers these challenges by usinga simple and accurate enhanced reconditioning equalizer filter chainmodule used at the input to this sub-system.

SUMMARY OF INVENTION

According to the invention, a low-cost enhanced reconditioning equalizerfilter chain, for use with any multi-carrier communication transmittersub-system, uses a plurality of simple and accurate algorithm inconjunction with intelligent signal processing to improve signalhandling of any wireless, optical, or wireline multi-carriercommunication transmitter. By intelligent, it is meant that thealgorithm has features of maintaining the signal emission and qualityrequirements while applying the enhanced reconditioning equalizer filterchain. The enhanced reconditioning equalizer filter chain uses thetransmitter sub-system input which could be a baseband, an IF or RFsignal as its input and conditions and smoothens the signal beforeapplying to the transmitter sub-system. The conditioning and smootheninghelps to boost the power handling of the transmitter sub-system or actsmore linearly. The inputs to the enhanced reconditioning equalizerfilter chain should be within a limit that can be handled by theenhanced reconditioning equalizer filter chain.

In a particular embodiment, the enhanced reconditioning equalizer filterchain algorithm comprises a signal processing module. The signalprocessor performs the signal conditioning and smoothening.

The invention will be better understood by reference to the followingdetailed description in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an overall block diagram of the enhanced reconditioningequalizer filter chain

FIG. 2 is the detail block diagram of the enhanced reconditioningequalizer filter chain

FIG. 3 is the detail block diagram of the enhanced reconditioningequalizer filter with configurable low pass filter in a firstfeedforward loop.

FIG. 4 is the detail block diagram of the enhanced reconditioningequalizer filter with adjustable out of band signal level through asecond feedforward loop.

DESCRIPTION OF THE SPECIFIC EMBODIMENTS

In a first preferred embodiment of the invention, the enhancedreconditioning equalizer filter chain uses sub-harmonic sampling toconvert RF or IF signals to digital baseband signal. In a secondpreferred embodiment the baseband signal is amplitude conditioned andsmoothened using a. enhanced reconditioning equalizer filter chain. In athird embodiment the enhanced reconditioning equalizer filter chainadjust the in band signal by configuring a low pass filter in afeedforward loop and the out of band signal by a stand alone feedforwardloop. In a fourth embodiment the multi-carrier baseband signal is downconverted to produce baseband representative of each individual carrier.In a fifth embodiment the multi-carrier baseband signal is peak reducedby a peak reduction filter. In a sixth embodiment the peak reducedmulti-carrier signal is down converted to produce peak reduced basebandrepresentative of each individual carrier. In a seventh embodiment theindividual baseband representation of the multi-carrier signal andindividual baseband representation of the peak reduced multi-carriersignal are applied to an enhanced reconditioning equalizer filter toproduce reconditioned and smoothen baseband representative of eachindividual carriers. In an eighth embodiment the reconditioned basebandrepresentative of each individual carrier is up converted and combinedto produce the reconditioned and smoothen multi-carrier baseband signal.In a ninth embodiment the out put of the enhanced reconditioningequalizer filter chain is used as the new input to the transmitsub-system.

Referring to FIG. 1, an enhanced reconditioning equalizer filter chaindiagram is illustrated. The enhanced reconditioning equalizer filterchain 200 receives its baseband input 100 and produce conditioned andsmoothened output 300. The enhanced reconditioning equalizer filterchain performs the following functions:

-   -   1. Reconditions and smoothens the amplitude of the input signal        100 before applying to transmitter sub-system.    -   2. Maintains the signal emission characteristic and quality.    -   3. Adjusts the gain in the signal paths to keep the total gain        from input to output of the enhanced reconditioning equalizer        filter chain unity.    -   4. Adjusts the out of band and in-band signal using a        configurable low pass filter in a feedforward loop or by a stand        alone feedforward loop.    -   5. Uses the individual baseband representatives of both main        multi-carrier signal and peak reduced multi-carrier signal to        recondition and smoothen the main multi-carrier signal.

FIG. 2 illustrate the detail block diagram of the enhancedreconditioning equalizer filter chain. The main multi-carrier basebandsignal 100 is applied to down converters DC10 function 102, DC20function 104, through DCn0 function 106 to produce the main individualbaseband representative 131, 133, through 135 of each carrier withinmain multi-carrier baseband signal. The main multi-carrier basebandsignal 100 is also applied to Peak Reduction Filter (PRF) function 101to produce peak reduced main multi-carrier baseband signal 130. Theamount of peak reduction is adjusted through parameter 267 supplied bycontroller 211. The peak reduced main multi-carrier baseband signal 130is applied to down converters D11 function 103, DC21 function 105,through DCn1 function 107 to produce the main individual carrierbaseband representative 132, 134, through 136 of each individual carrierwithin peak reduced main multi-carrier baseband signal. The firstcarrier's main baseband representative 131 and its peak reduced mainbaseband representative 132 are applied to enhanced reconditioningequalizer filter “1” function 108 to produce reconditioned and smoothenmain baseband representative 141. The reconditioned and smoothen mainbaseband representative 141 is up converted to its original basebandfrequency 151 by up converter UC1 function 111. The second carrier'sbaseband representative 133 and its peak reduced main basebandrepresentative 134 are applied to enhanced reconditioning equalizerfilter “2” function 109 to produce reconditioned and smoothened mainbaseband representative 142. The reconditioned and smoothened mainbaseband representative 142 is up converted to its original basebandfrequency 152 by up converter UC2 function 112. The Nth carrier's mainbaseband representative 135 and its peak reduced main basebandrepresentative 136 are applied to enhanced reconditioning equalizerfilter “3” function 110 to produce reconditioned and smoothened mainbaseband representative 143. The reconditioned and smoothen mainbaseband representative 143 is up converted to its original basebandfrequency 153 by up converter UCn function 113. The up convertedreconditioned and smoothened signals 151, 152, and 153 are combined insumming bock 114 to produce the reconditioned and smoothened mainbaseband signal 300. In FIG. 2 only three of “N” individual carrierbaseband representative of main baseband signal is shown.

FIG. 3 illustrates the detail block diagram of the enhancedreconditioning equalizer filter “1” unit with configurable low passfilter. The main baseband signal 131 (which is the basebandrepresentative of the main baseband multi-carrier signal) is delayed bydelay block 202 to produced delayed main baseband signal 251. Thedelayed main baseband signal 251 is gain adjusted by gain block 203 toproduce delay and gain adjusted main baseband signal 252. The delay andgain adjusted main baseband signal 252 is subtracted from peak reducedbaseband signal 132 (which is the baseband representative of the peakreduced main baseband multi-carrier signal) in subtraction block 204 toproduce baseband signal 253. The amount of delay 262 and gain adjustment263 are calculated by the correlation block 205 that uses main basebandsignal 131 and signal 253 as its input. The correlation block 205 alsoreceives a control signal 261 from controller block 211 to use tocalculate the delay amount 262 and gain adjustment amount 263. Thebaseband signal 253 is filtered by Low Pass Filter (LPF) block 207 toremove any out of band signal and produce in-band baseband signal 254.The coefficients of the Low Pass Filter (LPF) block 207 is configurableand supplied by controller 211 to adjust the amount of out of bandrejection. The coefficient parameters 266 from controller 211 used byLow Pass Filter (LPF) block 207 can be set during configuration orautomatically by monitoring the input signal 131 and output signal 141.The in-band baseband signal 254 is gain adjusted by gain block 208 toproduced gain adjusted in-band baseband signal 256. The amount of gainadjustment 265 is supplied by controller block 211. The main basebandsignal 131 is delay and gain adjusted by delay/gain block 206 to producedelay and gain adjusted main baseband signal 255. The delay and gainadjusted main baseband signal 255 and the gain adjusted in-band basebandsignal 256 are summed in summation block 209 to produce modified mainbaseband signal 257. The modified main baseband signal 257 is gainadjusted by gain block 210 to produced reconditioned and smoothenedbaseband signal 141. The main baseband signal 131 and the modifiedbaseband signal 141 are applied to controller 211 to provide the gainand delay parameters needed for the gain blocks and the correlationblock. The enhance reconditioning equalizer filters “2” through “N” areidentical to enhanced reconditioning equalizer filter “1”.

FIG. 4 illustrates the detail block diagram of the enhancedreconditioning equalizer filter “1” unit with adjustable out of bandsignal level. The main baseband signal 131 (which is the basebandrepresentative of the main baseband multi-carrier signal) is delayed bydelay block 202 to produced delayed baseband signal 251. The delayedbaseband signal 251 is gain adjusted by gain block 203 to produce delayand gain adjusted baseband signal 252. The delay and gain adjustedbaseband signal 252 is subtracted from peak reduced baseband signal 132(which is the baseband representative of the peak reduced main basebandmulti-carrier signal) in subtraction block 204 to produce basebandsignal 253. The amount of delay 262 and gain adjustment 263 arecalculated by the correlation block 205 that uses main baseband signal131 and signal 253 as its input. The correlation block 205 also receivesa control signal 261 from controller block 211 to use to calculate thedelay amount 262 and gain adjustment amount 263. The baseband signal 253is filtered by Low Pass Filter (LPF) block 207 to remove any out of bandsignal and produce in-band baseband signal 254. The in-band basebandsignal 254 is gain adjusted by gain block 208 to produced gain adjustedin-band baseband signal 256. The amount of gain adjustment 265 isapplied by controller block 211. The main baseband signal 131 is delayand gain adjusted by delay/gain block 206 to produce delay and gainadjusted main baseband signal 255. The delay and gain adjusted mainbaseband signal 255 and the gain adjusted in-band baseband signal 256are summed in summation block 209 to produce modified main basebandsignal 257. The modified main baseband signal 257 is gain adjusted bygain block 210. The baseband signal 253 is delayed by delay block 212 toproduce baseband signal 280. The baseband signal 280 is gain adjusted bygain block 213 to produce baseband signal 281. The amount of delayadjustment 271 for delay block 212 and gain adjustment 267 for gainblock 213 are supplied by controller block 211. The baseband signal 281is subtracted from baseband signal 254 in subtraction block 214 toproduce the out of band baseband signal 282. The out of band basebandsignal 282 is gain adjusted by gain block 215 to produced gain adjustedout of band baseband signal 283. The out of band baseband signal 283 isadded to main baseband signal 258 in summation block 216 to produce mainbaseband signal 259. The baseband signal 259 is gain adjusted by gainblock 217 to produce baseband signal 141. The amount of gain control 270for gain block 217 is supplied by controller 211. The main basebandsignal 131 and the modified baseband signal 141 are applied tocontroller 211 to provide the gain and delay parameters needed for thegain blocks and the correlation block. The enhance reconditioningequalizer filters “2” through “N” are identical to enhancedreconditioning equalizer filter “1”.

1. An enhanced reconditioning equalizer filter chain for multi-carriersignals to enhance the performance of any communication transmitter, anenhanced reconditioning equalizer filter chain for multi-carrier signalscomprising: a peak reduction filter to produce a peak reduced mainmulti-carrier baseband signal; a first down converter to down convert amain multi-carrier baseband signal to produce a baseband representativeof each individual carrier of the main multi-carrier baseband signal; asecond down converter to down convert the peak reduced mainmulti-carrier baseband signal to produce a baseband representative ofeach individual carrier of the peak reduced main multi-carrier basebandsignal; a reconditioning equalizer filter to re-condition and smoothenthe baseband representative of each individual carrier of the mainmulti-carrier baseband signal using the baseband representative of eachindividual carrier of the peak reduced main multi-carrier basebandsignal, wherein the reconditioning equalizer filter comprises: a firstfeedforward loop to inject a controlled in-band signal into the basebandrepresentative of each individual carrier of the main multi-carrierbaseband signal, comprising: a first gain element in a first feedforwardloop to adjust the gain of the baseband representative of eachindividual carrier of the main multi-carrier baseband signal; a firstdelay element in a first feedforward loop to adjust the delay of thebaseband representative of each individual carrier of the mainmulti-carrier baseband signal; a subtractor that subtracts the delay andgain adjusted baseband representative of each individual carrier of themain multi-carrier baseband signal and the baseband representative ofeach individual carrier of the peak reduced main multi-carrier basebandsignal; a correlation function to correlate the baseband representativeof each individual carrier of the main multi-carrier baseband signal andthe result of the subtraction of the delay and gain adjusted basebandrepresentative of each individual carrier of the main multi-carrierbaseband signal and the baseband representative of each individualcarrier of the peak reduced main multi-carrier baseband signal tocalculate the amount of the delay and gain adjustment for the basebandrepresentative of each individual carrier of the main multi-carrierbaseband signal; a digital FIR (or IIR) low pass filter withconfigurable coefficients to filter the result of the subtraction of thedelay and gain adjusted baseband representative of each individualcarrier of the main multi-carrier baseband signal and the basebandrepresentative of each individual carrier of the peak reduced mainmulti-carrier baseband signal; a second gain element to adjust the gainof the low pass filtered subtraction of the delay and gain adjustedbaseband representative of each individual carrier of the mainmulti-carrier baseband signal and the baseband representative of eachindividual carrier of the peak reduced main multi-carrier basebandsignal; a delay and gain adjustment element to adjust the delay and gainof the baseband representative of each individual carrier of the mainmulti-carrier baseband signal; a summer to add the delay and gainadjusted baseband representative of each individual carrier of the mainmulti-carrier baseband signal and the gain adjusted low pass filteredsubtraction of the baseband representative of each individual carrier ofthe peak reduced main multi-carrier baseband signal and the delay andgain adjusted baseband representative of each individual carrier of themain multi-carrier baseband signal; a third gain element to adjust thegain of the sum of the delay and gain adjusted baseband representativeof each individual carrier of the main multi-carrier baseband signal andgain adjusted low pass filtered subtraction of the basebandrepresentative of each individual carrier of the peak reduced mainmulti-carrier baseband signal and the delay and gain adjusted basebandrepresentative of each individual carrier of the main multi-carrierbaseband signal; an upconverter that up converts the reconditioned andsmoothened baseband representative of each individual carrier of themain multi-carrier baseband signal to its baseband signal frequency; asummer that sums all of the up converted, reconditioned, smoothened anddelay equalized baseband representatives of each individual carrier ofthe main multi-carrier baseband signal to produce the reconditioned andsmoothened main multi-carrier baseband signal; a controller that usesthe baseband representative of each individual carrier of the mainmulti-carrier baseband signal, the output of the enhanced reconditioningequalizer filter for the baseband representative of each individualcarrier of the main multi-carrier baseband signal, and externalinformation to provide control signal to various delay and gainfunctions as well as the peak reduction filter, FIR low pass filter andthe correlation function.
 2. An enhanced reconditioning equalizer filterchain for multi-carrier signals according to claim 1, wherein anenhanced reconditioning equalizer filter used in the filter chainfurther comprises: a second feedforward loop to inject a controlled outof band signal into the main baseband representative of each individualcarrier of the main multi-carrier baseband signal, comprising: a fourthgain element to adjust the gain of the subtraction of the delay and gainadjusted baseband representative of each individual carrier of the mainmulti-carrier baseband signal and the baseband representative of eachindividual carrier of the peak reduced main multi-carrier basebandsignal; a second delay element to adjust the delay of the subtraction ofthe delay and gain adjusted baseband representative of each individualcarrier of the main multi-carrier baseband signal and the basebandrepresentative of each individual carrier of the peak reduced mainmulti-carrier baseband signal; a second subtractor to subtract the gainand delay adjusted subtraction of the delay and gain adjusted basebandrepresentative of each individual carrier of the main multi-carrierbaseband signal and the baseband representative of each individualcarrier of the peak reduced main multi-carrier baseband signal and thelow pass filtered subtraction of the delay and gain adjusted basebandrepresentative of each individual carrier of the main multi-carrierbaseband signal and the baseband representative of each individualcarrier of the peak reduced main multi-carrier baseband signal; a fifthgain element to adjust the gain of the subtraction of the gain and delayadjusted subtraction of the delay and gain adjusted basebandrepresentative of each individual carrier of the main multi-carrierbaseband signal and the baseband representative of each individualcarrier of the peak reduced main multi-carrier baseband signal and thelow pass filtered subtraction of the delay and gain adjusted basebandrepresentative of each individual carrier of the main multi-carrierbaseband signal and the baseband representative of each individualcarrier of the peak reduced main multi-carrier baseband signal; a summerto add the reconditioned and smoothened baseband representative of eachindividual carrier of the main multi-carrier baseband signal from afirst feedforward loop with the second feedforward loop gain adjustedsubtraction of the gain and delay adjusted subtraction of the delay andgain adjusted baseband representative of each individual carrier of themain multi-carrier baseband signal and the baseband representative ofeach individual carrier of the peak reduced main multi-carrier basebandsignal and the low pass filtered subtraction of the delay and gainadjusted baseband representative of each individual carrier of the mainmulti-carrier baseband signal and the baseband representative of eachindividual carrier of the peak reduced main multi-carrier basebandsignal; a sixth gain element to adjust the gain of the sum of theconditioned and smoothened baseband representative of each individualcarrier of the main multi-carrier baseband signal from a firstfeedforward loop with the second feedforward loop gain adjustedsubtraction of the gain and delay adjusted subtraction of the delay andgain adjusted baseband representative of each individual carrier of themain multi-carrier baseband signal and the baseband representative ofeach individual carrier of the peak reduced main multi-carrier basebandsignal and the low pass filtered subtraction of the delay and gainadjusted baseband representative of each individual carrier of the mainmulti-carrier baseband signal and the baseband representative of eachindividual carrier of the peak reduced main multi-carrier basebandsignal.
 3. An enhanced reconditioning equalizer filter chain formulti-carrier signals with different technologies according to claim 2,wherein the out of band signal of the baseband representative of eachindividual carrier of the main multi-carrier baseband signal is adjustedby a second feedforward loop that injects an adjustable out of bandsignal into the baseband representative of each individual carrier ofthe main multi-carrier baseband signal.
 4. An enhanced reconditioningequalizer filter chain for multi-carrier signals according to claim 1,wherein the controller using the input and the output of thereconditioning equalizer filter controls the delay and gain adjustmentelements used in the reconditioning equalizer filter.
 5. An enhancedreconditioning equalizer filter chain for multi-carrier signalsaccording to claim 1, wherein a Digital Signal Processing (DSP) functionis implemented in programmable logic, Field Programmable Gate Array(FPGA), Gate Array, Application Specific Integrated Circuit (ASIC), orDSP processor.